This is a project to test the basic idea that T cells reacting to somatically generated sequences in autoantibody variable regions mediate the development of pathology in lupus nephritis (LN). Many years of research into the immunobiology of LN have demonstrated the pathologic capacity of B cells, infiltrating T cells, and immune complexes in the glomerular endothelium. Inflammatory kidney-infiltrating T cells, both IFN3-secreting Th1 and IL-17-secreting Th17 cells, recruit innate effector cells, which inflict damage upon glomerular cells. However, the mechanisms by which T cells are primed, the specificity of renal T cells, and how autoantibodies are initially elicited are still large unanswered questions. I hypothesize that these questions can be explained by T cells that react to MHC II-presented peptides derived from autoantibodies and that differentiate into inflammatory mediators of kidney pathology. The significance of this hypothesis applies not only to genesis of disease but also to its treatment, as human anti-chimera antibodies (HACA) driven by antibody peptide-specific T cells may play a role in the unexpectedly variable response of LN to monoclonal antibody therapy. To test this hypothesis, I will use an adoptive transfer model of SLE with nephritis in which T cells specific for a V: peptides are introduced into a mouse expressing a corresponding Ig: transgene in B cells. I will determine whether nephritogenic Th1 and Th17 T cells that later arise in mice with LN are V: peptide-specific or instead are derived from an endogenous population via determinant spreading. Both V: peptide-specific and endogenous CD4 T cells will be assessed for microanatomical localization and for their participation in conjugate formation with Ig: transgenic B cells in the kidney. I will extend this analysis to anti-glomerular basement membrane (GBM) models of LN, in which T cell populations in the kidneys may be responsive to either autologous or heterologous antibodies. Finally, I will test the hypothesis that IgG in immune complexes is immunogenic and proinflammatory for V: peptide-specific T cells, and that this is dependent upon Ig glycan content. In contrast, I predict that IgM is immunogenic but noninflammatory. The results of this work will reveal important information about potential antigenic specificities of nephritogenic T cells and provide insight into mechanisms that promote HACA responses in patients that receive monoclonal Ab therapy.